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ST eFuse (electronic fuse) User guide

  • Hello! I'm your chat assistant. I've reviewed the STMicroelectronics eFuse quick reference guide and understand the specifications and features of the eFuses described in it, including models like STEF01, STEF12, STEF05 and others. I'm here to help you with any questions regarding their functionality, protections, and various parameters. Feel free to ask me about soft start, overcurrent limits, or anything else detailed in the document.
  • What is an eFuse?
    What does the dV/dT pin do?
    What is the enable/fault pin for?
    What is the purpose of the "Soft Start" feature?
    What does UVLO stand for?
Order code: BR2201EFUSEQR
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5
GLOSSARY AND DEVELEOPMENT TOOLS
DEMOBOARDS
Accuracy – the maximum deviation from the specied over voltage, and over current protection levels.
Auto-retry – an auto-retrying device will turn itself back on after a thermal shutdown once the die temperature is below the
hysteresis value.
Bias current – the current needed by the eFuse itself to maintain operation.
Overload current limit, or current limit trip-point – the eFuse reacts to overcurrent events by reducing the conductivity of the
pass element once the current exceeds this limit.
Short circuit current – when a strong overload occurs and the output voltage drops as a consequence, the device limits the
current to a level below the regular current limit.
dV/dT – this refers to the internal circuitry that controls the output voltage rise at turn-on. The external dV/dT pin allows the
user to adjust the soft-start time.
Enable-fault – the enable-fault pin is a dual-function pin: it lets the user enable and disable the device, and at the same time
provides the device status through a three-state logic.
Gate driver – to protect the supply and pass element, STEF01 and STEF12S include an internal charge pump to drive an
external MOSFET that prevents reverse currents and large transient voltages which may occur during high-current limiting.
Hysteresis – to prevent an auto-retrying device from repeatedly turning ON and OFF after a thermal shutdown, the device only
turns back on once the temperature has dropped by the hysteretic value.
Latch – when a thermal fault occurs, the device will remain OFF until the power or enable-signal is cycled by the user.
Output Voltage Clamp – if the input voltage exceeds the pre-dened voltage clamp value, the internal protection circuit
ensures the output voltage does not rise above this preset value.
Pass element – the voltage and current pass through a low-resistive power MOSFET which can be controlled to limit the
output current and voltage in reaction to fault conditions.
Power dissipation – during normal operation, the power dissipated by the device depends on the pass element’s RDS(on) and
the load current. When voltage/current is regulated, which happens during start-up and in case of faults, the excess power is
dissipated in the form of heat. In persistent faulty conditions, this heat shuts the device down as a consequence of thermal
protection.Thermal design and correct soft-start congurations are important to prevent unwanted shutdowns, which are most
likely to occur during start-up phases or in high and continuous current conditions.
Power Good (PG) – a signal to indicate that the output voltage is very close to the input and that no current/voltage limitation
is in place. It can be used for power-sequencing, reset-triggering, and more.
Soft Start (SS) – a Soft Start is a controlled delivery of the output power , which minimizes inrush currents, thus protecting the
power supply from overloading. The Soft Start time can be extended by adding a capacitor to the dV/dT pin.
Thermal shutdown – during a persistent fault, the eFuse die will heat up. Once the shutdown temperature (typically 175°C) is
reached, the device will turn off the internal pass element and go in latch or auto-retry state.
UVLO (Undervoltage lockout) – the UVLO makes sure the device does not turn on until the supply voltage is high enough, thus
contributing to the eFuse’s predictable and reliable performance.
For more information, visit us on www.st.com/efuse
Part number Product Description
STEVAL-EFUSE01 STEF01 Evaluation board based on the STEF01 fully programmable universal electronic fuse
STEVAL-IFP021V1 STEF12/STEF05 5 V and 12 V power line protection based on STEF05 and STEF12 electronic fuses
eFuse (electronic fuse)
Quick reference guide
2
eFuses PORTFOLIO OVERVIEW
HOW DOES AN eFuse WORK ?
KEY FEATURES
PACKAGE RANGE
Ensuring safer designs and more efficient applications
An eFuse is a low-resistance switch connected in series to the main
power rail and controlled by logic circuitry to protect loads and power
supplies. Smaller, faster and more efcient than conventional fuses
or polymeric PTCs, eFuses detect and react to overcurrent and
overvoltage conditions, and do not require replacement after a fault
event.
Quick and intelligent response to faults
Unlike conventional fuses, which are based on the principle that a conductor will overheat and melt during an overload
condition, the eFuse only clamps the output voltage and/or limits the throughput current, thus allowing the device to be
supplied correctly, before eventually disconnecting the load in case of persistent failure. This prevents load and supply
damage from occurring and avoids false triggering caused by transient conditions. Moreover, in applications powered by DC
buses, eFuses reduce the bus droop due to faulty loads, avoiding the propagation of nuisance or undervoltage to other loads
connected to the same bus.
Reduced maintenance
Since eFuses do not sacrice their pass element, they can immediately be reset with a signal from the system by either cycling
the supply power or by simply waiting, if auto-retry is used. The equipment’s uptime is maximized and the cost and complexity
of maintenance are reduced.
Inrush current control
Inrush current conditions can occur during start-up or hot-plugging. eFuses ramp the output voltage up in a controlled manner
to prevent large inrush currents from overloading the power supply. This feature is crucial when multiple loads are supplied by
a single power supply.
Flexible application design
Every eFuse can be programmed and tailored to your specic needs. Most eFuses allow users to set the current limit and
start-up time. The undervoltage lockout and output clamp levels as well as the device’s operating mode (latch-off or auto-retry
mode) can also be congured on certain part numbers.
When an overload or short-circuit condition occurs, the eFuse limits the current to a pre-dened safe value. When an
overvoltage condition occurs, the eFuse clamps the output voltage to a safe level,thus protecting the load from abnormalities
caused by malfunctioning power supplies.
The eFuse disconnects the load from the power supply if fault conditions are persistent. Depending on the version, the device
operates either in latch-off mode, which means it is switched-off and must be re-armed manually, or in auto-retry mode
where the device will automatically re-start.
Output voltage clamping
Each eFuse has a predened maximum output voltage safe value.
If the input voltage exceeds this value, the eFuse clamps the output
voltage to the preset value and allows the device to operate without
damaging the load or system.If the overvoltage is persistent, the eFuse
disconnects the load.Most eFuses have a pre-set voltage clamp value.
The STEF01 allows users to congure it.
Current limiting
When an overload condition occurs, the eFuse reduces the
conductivity of the internal pass element to effectively limit the
current to a precongured value. If a strong overload or short circuit
occurs, the device enters the foldback current limit, and eventually
disconnects the load, thus protecting the power supply. This value is
usually congured using an external resistor.
Undervoltage lockout
The undervoltage lockout feature disconnects the load from the
supply if the input voltage is lower than a preset minimum. By avoiding
issues caused by too low supply voltage such as wrong voltages from
bandgap references, incorrect control signals in logical circuitry, and
transistors being only partially ON or OFF, the undervoltage lockout
increases system predictability.The STEF01 allows users to set the
undervoltage lockout threshold between 8 V and 45 V.
12 V, 60 A High precision eFuse with 0.85 mW RDSON current and
temperature monitor pins. Parallel conguration.
QFN 32 5x5 package
12 V, 4 A high-precision simple eFuse
TSOT23-8L and DFN 3x3 packages
5 V, 4 A high-precision simple eFuse
TSOT23-8L package
5 V + 12V in one 3 A eFuse
TSOT23-8L package
5 V + 12 V in one 3 A eFuse with current monitor
QFN 2x3 package
5 V + 12 V in one 3 A eFuse with reverse current protection
on 5V channel
DFN 2x3 package
8 – 48 V, 4 – 5 A Fully programmable eFuse with 30 mW RDSON
HTSSOP14 package
Turn-on delay/Soft start
The eFuse provides a dened and predictable ramp-up of the output
voltage during start-up, to ensure the inrush current is maintained
within safe connes and protects both the load and the power
supply.The soft start duration can be easily congured by an external
capacitor.
Enable/Fault pin
All eFuses feature an enable/disable pin, to turn-on/off the device. In addition, some products offer the
enable/fault pin, which is a dual-function pin that allows users to manually turn the output off and to read
the current state of the device. The eFuse can be reset by toggling this pin after a thermal shutdown.
The pin can be used as a regular enabling pin and can be connected to a monitoring circuit to notify
thermal shutdown events. It can also be connected to the Enable/Fault pins of other eFuses, to achieve a
simultaneous Enable/Disable operation for all devices.
VOUT / Source
R-lim
I-limit
dV / dT
IN EN / Fault
OUT
STEF12
COUT
VCC
LOAD
Controller
CIN
Control &
Protections
KEY BENEFITS OF ELECTRONIC FUSES
High Power
• SERVER
• TLC infrastructures
• Industrial controls
• NAS/SAN
•
Low Power
• Data-storage
• Industrial
• Consumer
12 V
48 V
Transient voltage
Output voltage
Voltage clamp level
Short limit
Load current
Trip point
Input voltage
Lockout threshold
Output voltage
Enable signal
Input voltage
STEF01
STEF12S
STEF05S
STEF512GR
STEF512SR
STEF512PUR
STEF12H60M
12 V
5 V
Dual
3.3
5
12
48
80
1.5 3 4 5 7 24 60
Power Breaker Standard eFuses Dual rail 5 V + 12 V Fully programmable 3,3 V or 5 V rail
Low side timed switch High power eFuse
High power load switch
Continuous current (A)
(Not to scale)
Typical voltage rail (V)
(Not to scale)
Legend:
STEF033
STEF12S STEF12H60M
STEF05S
STEF05
STEF05D
STEF05L
STEF512GR
STEF512PUR
STEF512SR
STEF4S
STEF01
STEC01
(Safety IC)
STEL12H24
STPW12 STEF12
STEF12E
DFN 2x3 10L QFN 2x3 10L DFN10 3x3
HTSSOP14 QFN 32 TSOT23-8L
/